Organic peroxyacids are useful as fabric bleaching agents but are highly reactive compounds of limited storage stability. Storage stability refers to the extent to which the available oxygen (AvO) content of the peroxyacid is maintained over time.
Heretofore, generally three ways of improving storage stability of peroxyacids have been employed: chelants, pH control, and moisture control. The chelants combine with any metal ions present and thus prevent any decomposition of the peroxyacid which would be catalyzed by heavy metals. Seven references are representative: U.S. Pat. No. 4,170,453, Kitko, issued Oct. 9, 1979; U.S. Pat. No. 4,091,544, Hutchins, issued May 30, 1978; U.S. Pat. No. 4,100,095, Hutchins et al., issued July 11, 1978; U.S. Patent 4,126,573, Johnston, issued Nov. 21, 1978; U.S. Pat. No. 4,259,201, Cockrell, Jr. et al., issued Mar. 31, 1981; U.S. Pat. 4,325,828, Postlethwaite, issued Apr. 20, 1982; and European Patent Application No. 0068547, Bossu et al., filed June 9, 1982.
The preferred chelating stabilization system in these references is a mixture of 8-hydroxyquinoline or dipicolinic acid and an acid polyphosphate. Although chelants reduce or eliminate the problem of decomposition caused by heavy metals, they do not address the problem of decomposition of acid-sensitive peroxyacids caused by the acidic environment remaining after synthesis of the peroxyacid.
Several references suggest pH control as a way to optimize stability of bleach and/or detergent compositions. See European Patent Application No. 0176124, de Jong et al., published Apr. 2, 1986 (pH 3.5-4.5); European Patent Application No. 0201958, Meijer et al., published Nov. 20, 1986 (pH 4.1); U.S. Pat. No. 4,287,135, Stober et al., issued Sept. 1, 1981 (pH 2-6 and coating with reaction mixture); and European Patent Application No. 0200163, Jacobs et al., published Nov. 5, 1986 (pH 3-7). The last reference also includes a polymer coating of the bleach granule. All of these references except Stober et al. also include chelants.
European Patent Application No. 0212976, Coyne et al., published Mar. 4, 1987 teaches improved peracid stability through control of water levels during synthesis of peracid.
With an acid-sensitive peroxyacid such as an amidoperoxyacid, it is especially important that a way be found to make the peroxyacid stable for storage. Otherwise, the amidoperoxyacid, even with known storage stabilizers such as those described above, will decompose over time. It has been found that contacting the amidoperoxyacid with phosphate buffer at a pH between about 3.5 and 6, preferably between about 4 and 5, just after synthesis of the amidoperoxyacid, significantly slows this decomposition. Although this process is simple, it has heretofore not been used to stabilize peroxyacid. The amidoperoxyacid washed in phosphate buffer remains stable even when incorporated into an alkaline detergent composition, which is also surprising.
Amidoperoxyacids, or peroxyacids with a polar amide link in the hydrophobic chain, are described in U.S. Pat. No. 4,634,551, Burns et al., issued Jan. 6, 1987, and U.S. Pat. No. 4,686,063, Burns, issued Aug. 11, 1987. Such amidoperoxyacids have the following general formulas: ##STR1## wherein R.sub.1 and R.sup.2 are alkyl(ene), aryl(ene) or alkaryl(ene) groups containing from about 1 to about 14 carbon atoms and R.sup.5 is H or an alkyl, aryl, or alkaryl group containing from about 1 to about 10 carbon atoms.
Sulfone peroxyacids, which are generally more stable than amidoperoxyacids, are represented by the following formula: ##STR2## wherein A and B are organic moieties bonded to the sulfur atom by a carbon atom and at least one of A and B containing at least one ##STR3## group bonded to a carbon atom. Sulfone peroxyacids are disclosed in European Patent Application No. 0267175, Dyroff et al., published May 11, 1988. In Example 4 of that application a methylene chloride solution of the sulfone peroxyacid was washed with phosphate buffer solution, then washed with water, partially evaporated and mixed with boric acid as a part of a series of steps.
It is an object of the present invention to provide a means of improving the storage stability of amidoperoxyacids.
It is also an object of the present invention to provide a means of improving amidoperoxyacid storage stability in a detergent composition.